The word is of a low-register (eg. slang) so it's best to avoid it generally.

People in favour of conserving the language will object to any example of its usage but language change cannot be controlled effectively and if it becomes popular then (unfortunately) that is just the way it's meant to be.

Well, it's more like children to say that or people who got into the habit. That's just my personal opinion and I'm not all that articulate, I just think it's best to avoid bad habits before they become ingrained. Another thing: It mostly comes with a negative overtone, like - בוא'נה watch your mouth, or בוא'נה I'm not your your friend (so don't talk to me like you do)
And when it doesn't it's completely uncalled-for, as in: בוא'נה have you seen the new Ben Stiller movie? or בוא'נה have you heard what happened at the mall yesterday?

בוא'נה/בואנה is considered slangy, but I wouldn't go as far as saying you should never use it.
It's composed of "בוא הנה" which literally means "come here", but it actually states a surprise to the thing it precedes.

For instance:
בואנה, זה לא זול = "wow/mmm, that's not cheap (I did not expect this price)" sorry I can't think of a term that conveys the whole idea of it.

I guess you could think of it as: "come here and look!" which stays true to the Hebrew version, but hardly captures the easygoing/light feeling of בואנה.
I keep coming up with more examples of its uses but I'm having trouble translating them. Maybe our fellow board members will contribute.

Anyway, it's a very (very) popular word nowadays. You hear it all the time in conversations/radio commercials, sometimes even on TV ads.

To its defense, I'd say בואנה is not at the top of my "worst slang words which have got to disappear" list.
Use it or not, it doesn't matter. it has rooted strongly in the everyday speech of Israeli Hebrew.

There are situations where בואנה fits perfectly with the idea you're trying to convey, and even sets a comical mood to your sayings.

I understand the term as a vulgar way to call somebody or to begin conversation with him,
and is used between children or friends.
The use can be friendly "?בוא'נה איך הצלחת לעשות את זה" or unfriendly "?בוא'נה שמעת מה אמרתי לך".